Fuel burner assembly



July 20, 1965 s. c. WHITNEY, JR

FUEL BURNER ASSEMBLY 3 Sheets-Sheet 1 Filed Dec. 21, 1962 I ll////// r/r/ l A TTOR/Vfy J ly 1955 G. c. WHITNEY, JR

FUEL BURNER ASSEMBLY 3 Sheets-Sheet 2 Filed Dec. 21. 1962 .1: 1NVENTOR. N 67/455 976. Pl HITNEY, JR.

A TTORNE Y July 20, 1965 G. c. WHITNEY, JR

FUEL BURNER ASSEMBLY 3 Sheets-Sheet 3' Filed Dec. 21, 1962 I l I I I l 5 6 35E 2. 3235.31 muzmam AVERAGE VELOC|TY..

HEAD IN BURNER THROAT .6

9N loll Ill! lzll VANE LENGTH m INCHES AIR FLOW=30,000 LBSIHR AT 70F.

INVENTOR. G/LBEAT a by/7W5; JR.

M/M/ZM A TTOENE Y United States Patent 3,195,483 FUEL BURNER ASSEMBLY Gilbert C. Whitney, In, Dansville, N.Y., assignor to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Fiied Dec. 21, 1962, Ser. No. 246,503 1 Claim. (Cl. 110104) This invention relates to a fuel burner assembly, and more particularly to a fuel burner which uses pulverized solid fuel.

The burn-er assembly to which the invention relates is of the type wherein the burner is disposed adjacent a burner port in a furnace wall and is oriented to project a fuel jet into the furnace. Air for the combustion of the fuel may be injected with the fuel through the burner nozzle, but additional or secondary air is also supplied around the burner nozzle.

In the past, it has been an objective in burners to balance the velocities of the secondary air and fuel against the burning rate of the fuel so that the flame is concentrated at a desired distance from the burner throat. It is now realized, however, that when the velocities of the secondary air and the fuel are approximately equal, the fuel remains too dense a mixture to burn, and that a more controlled flame can be obtained by using different velocities for the fuel and secondary .air for a rapid dispersion of the fuel into the air stream. Generally, a higher velocity for the secondary .air is desired, but this necessitates a uniform distribution of the air around the burner nozzle. A nonuniform distribution may cause a portion of the fuel to burn too early and too close to the burner nozzle with possible injury to the Wall tubes surrounding the nozzle.

This is particularly important in the combustion of fuel for steam generators wherein the furnace section of the generator is,relatively small and the path of the burning mixture from the mouth of the burner to a tube bank of the steam generator is relatively short.

To obtain uniform distribution of secondary air, it is well known in the art to surround the burner nozzle with a sleeve arrangement defining an annular passageway through which the air flows. One such arrangement is illustrated in Patent No. 2,912,942, issued to G. C. Whitney, et. al., dated November 17, 1959. In the-arrangement of this patent, the annulus surrounding the burner is defined in part by the burner nozzle and in part by a baffle arrangement, the inlet end of which is in communication with a windbox, and the outlet end of which is in communication with the burner nozzle outlet.

In present day generators, the windboxes required for these units are made .as small as possible since it is uneconomical to make them too large. The air enters the windbox from one side, with the result that it converges on one side of the annular passageway surrounding the burner and is nonuniformly distributed into the burner port. Obviously this results in nonuniform combustion of the fuel mixture.

Prior researchers in the field have taken the approach that throttling or baffling the inlet end of the secondary air passageway will provide uniform distribution of the secondary air around the burner nozzle. One such approachis described in Patent No. 2,480,5 47, issued to Vergenius L. Caracristi. In this patent, the inlet end of the passageway is in communication with a wind box through a circumferential radially directed port. A cylindrical sleeve of larger diameter than the circumferential port is disposed over the port to cause the secondary air to take a somewhat tortuous pat-h. An additional baffle plate is disposed across the path of the air so that this latter plate plus the tortuous path equalizes around the burner the ice resistance to air flow of the secondary air for uniform distribution of the air.

A principal disadvantage with an arrangement of this type is that the resistance to secondary air flow is substantially increased with a resulting power loss. Another disadvantage is that the distribution of air is not always uniform with variable load conditions on the burner.

These and other disadvantages are overcome in accordance with the present invention in which a novel burner assembly is provided comprising a windbox or housing arranged adjacent to .a burner port and adapted to receive combustion air from a suitable source, usually under pressure. An elongated fuel burner nozzle extends through the housing having an outlet and projecting into the burner port for the discharge of fuel for combustion. Surrounding the burner nozzle, which preferably has a frustoconical configuration, an elongated annular secondary air passageway is provided defined by the burner nozzle and a ring-shaped annular bafiie coaxial with and encompassing the nozzle. The baffle preferably has a long-radius curvature so that the passageway extends from a large circumference inlet or register end in communication with the Windbox to a small circumference outlet or throat and in communication with and surrounding the burner nozzle discharge end. The register 1 rea of the secondary air passageway is proportioned so that it is approximately one and a half (1%) times the area of the passageway throat area.

It was found that this structure provided a substantially improved distribution of secondary air and a reduction in pressure drop over prior units. The reason for this is believed to be that, as the area of flow is decreased from the register area to the throat area, the velocity of the fluid must increase for an overall pressure drop through the passageway. This pressure drop and resultant velocity increase effects an even distribution of the secondary air in the region of the register proper, but in contradistinction to prior developments, and by virtue of a relatively free-flow long radius curvature passageway, this pressure drop is converted into the increased velocity of the secondary air, rather than being dissipated in needless turns and turbulance before reaching the burner throat. Accordingly, although a pressure drop is used to achieve the uniform distribution of the secondary air, the overall system resistance can be decreased, or at least not increased. 1

This is extremely important when it is realized that the flow of secondary air is approximately ten times by weight that of the primary air flow.

The above will become more evident with subsequent reference to test results, which show in brief that by using an unobstructed register area with a long radius curvature passageway and by decreasing the register area from an initial large area relative to the throat area, the pressure drop, instead of increasing, surprisingly decreased, until a critical point was reached for minimum pressure drop and optimum distribution of the secondary air. This point was found to be that where the ratio of register area to throat area is about 1 /211.

Preferably, the register or inlet end of the secondary air passageway is a circumferential, radially directed annular opening, in which, however, a plurality of vanes may be disposed to impart a circular or rotational motion to the secondary air stream. A small vane adjustment increases the difference between velocity components of the secondary air stream and the fuel, for improved dispersion of the fuel, without a marked variance in the ratio of register area to throat area, or marked increase in pressure drop of the secondary air.

In an embodiment of the invention, wherein the passageway extends from a large circumference end in communication with the windbox to a small circumference a a) end in communication with the: discharge end of 7 burner nozzle, the tubular member defining theouter side of the passageway may be pivotally adjustable about a point approximately located in .the plane of the burner nozzle outlet, or slightly in front of'the nozzle, and along the axis of the nozzle, for varying the direction of .the secondary air stream. The manner in which this outer member is pivoted is described in copending application Serial No. 847,596, filed October 20, 1959, now aban doned, by Gilbert C. Whitney and Kenneth E, Lee. I

In this embodiment, the register, which again has-an area about one and a half times the throat area, pivoted with the, outer tubular member so thatrthe area or an-:

the V nulus surrounding the burner nozzle is maintained substantially constant and the secondary air passageway substantially uniform. This in turn maintains the desired ratio of the register area to throat area. The combined effects of a'uniformpa'ssagewayand annulus and a con- ;stant ratio of register area to throat area result in an optimum distribution of secondary air at all positions of the tubular member. In addition, the secondary air stream velocity aroundthe burner nozzle is uniform for uniform dispersion of the fuel in the air producing a well shaped flame. At the same time, therabove provides a precise ccntrol over the direction of the secondary air stream and in turn, through a slight adjustmentof this direction, pre

cise control over the direction ofthe burner flame.

Other details of the invention and'advant'ages thereof will become more apparent upon consideration of the following specification, and accompanying v drawings 'in which: I y FIGURE 1 is a section elevation View of one of a plurality of fuel burner assemblies in accordance with the present invention; 7

FIGURE '2: is a section view taken along line 2'2 of FIG. 1 on a reduced scale of the fuel burner assembly of the present invention with parts in elevation for illustration purposes; j,

FIGURE 3 is a section view in elevation on an enlarged scale of an embodiment in accordance with the invention; and i 7 FIGURE 4 is a graph illustrating advantages of the invention.

Referring to FIGS. 1 and 2, the reference character 12 designates a fuel burner for pulverized fuel comprising a burner nozzle 14 having an inlet end 16, and outlet;

. V '4 small diameter end 4 8 in contact withthe walls of the burner port to a largediameter end extending into the wind-box plenum chamber 42. Theyopposing side of the passageway is defined by a washer-shaped plate 52 spaced from the large diameter end fifl of the baffle 46 and lying in a plane perpendicular to the axis of the burner nozzle, the inside periphery 54 of the plate being welded to the nozzle 14 at a point upstream of the discharge end 18. The remaining inner surface of the passageway is defined by the tapered endportion 55 0f the .burner nozzle 14 adjacent the discharge end 18. I

The above arrange'ment is such that the plate 52'and baffle 46 define'between them adjacent the large diameter end 5%) of the bafiie a circumferential register opening 56 whichis radially directed relative to the axis of the burner nozzle into the plenum chamber 42. v a In accordance with the invention, the area of the register opening'is arranged to be approximately one and a half times the area of the passageway throat area, designated by the numeral 58, between the burner nozzle end 13 and bafile 46. V 5

Within the register opening56, a plurality of vanes 60 are mounted onshafts 62 for rotation within the register area, the vanes'being disposed uniformly around the burner to impart to the incoming secondary air a clock.-

wise or counterclockwise rotational movement as desired.

'1 he vanesare interconnected to turn .an'equal amount,

the-vane on shaft 64 acting as a master vane positioned by handwheel assembly 66. p, 1

It should now be apparent thatthe secondary air entering the plenum chamber through inlet 70 in a vertical direction from the bottom side thereof, the chamber of nozzle.-

or dischargeend 18, and a volute section 29 connected to a pulverized fuel and air feed pipe 22. The nozzle '14 of the fuel burner comprises a frusto-conical shaped casing 24 which tapers gradually towards the axis thereof from the inlet 16 to the discharge end 18. Within the casing 24, a frusto-conical inner sleeve 26 coaxial with the nozzle casing is provided defining with the casing a generally tapered annular passageway 28 forthe fuel and air between the inlet 16 and the discharge end 18.

The burner nozzle 14 may be provided with spaced ribs 3% on the interior surface of the casing as disclosed in Patent No. 2,912,942 (supra). A suitable ignitor 32 and electrode tube 34 may be provided within the inner sleeve 2-6; i

Surrounding the nozzle 14 of the The annular secondary air passageway 44 is defined on' one side by anouter open-sided bell-shaped skirt or baffle 46 having a long radius curvature and extendingfrom a fuel burner, a windbox assembly generally designated by the numeral 36 is necessity being small in size, and communicating in turn with other adjacent burners will bepmore or less unevenly distributed in the chamberwith the change in direction to. horizontal flow parallel to the axis of the burn- Reducing the sizeiof the register area creates a resistance to flow. This resistance in combination with that created in increasing ,thevelocityfrom the register to the throat, provides an overall optimum resistance which equalizes the distribution of the flow around the burner By providinglan unobstructed register opening with a smoothlongradius curvature for the secondary air passageway, this pressure drop, -howevcr, is converted into .an increased velocity for the secondary air, rather than being dissipatedin needless turns and turbulence. Quite surprisingly, it was found that an' optimum or initial point existed where the ratio of register area to throat area provided a minimum overall pressuredr-op with optimum distribution of the secondary air.

This'is illustrated on FIG. 4 showing testresults obtainedduring a series of tests conducted with an air flow rate of 30,000 pounds per hour at F., using different register'areas defined by vane'ilength, i.e., the distance between the baflie end SO and-the plate 52. This graph.

'rotative angle were interpolated for measurements at various locations. With .a vane, length of about 11 inches, it was found that the air velocity variedfrom'425 feet per second to. velocities too low to measure in many locations and angular variation was equally erratic. Changing the vane setting to increase or decrease the angle of rotation seemed to have. very little effect'on the erratic pattern achieved. On the otherhand, properly proportioning the vane size or register area to the throat area not only ance, but also an improvement in velocity symmetry.

As an important aspect of the invention, it was found that the above invention concepts were equally applicable or effective at different air flow rates and load conditions.

It might be noted that reducing the vane length to 4 inches resulted in excellent velocity and angle distribution, but improvements in these respects did not warrant or justify the extra system resistance.

It was found that the vanes 60 could if desired be eliminated, their purpose being to impart a rotational flow to the secondary air stream. If properly designed, however, they offer little resistance to flow and a setting closed slightly from a fully opened position may improve burner characteristics, and provide means for removing some of a group of burners from service.

FIG. 3 illustrates an embodiment of the invention in which the direction of flow of the secondary air can be varied for control of the direction of the burner flame.

Referring to FIG. 3, the outer baffle 72 of the second ary air passageway 73 is supported in spaced relationship with the burner nozzle 24 by four radially extending arms 74 which are spaced at 90 from each other around the periphery of the baffle, the arms 74 extending radially from the bafiie slightly beyond the register opening 76. The distal end portions of the arms are connected to adjustment assemblies 78, which comprise actuating rod members 80 extending through the windbox plenum chamber 42, through sleeves 82 secured to the windbox, to handwheels 84. By suitably adjusting the handwheels, the rods 80 move axially within the sleeves 82 to pivot the baflie 72 about a point disposed slightly in front of the plane of the burner nozzle outlet or discharge end 18 and coaxial with the axis of the burner nozzle.

In order to obtain equal velocity components in the secondary air stream in the annulus around the burner nozzle, and thus a well-shaped flame, it is essential that this annulus be maintained uniform in cross-section. To do this, the baffle 72 should be pivoted about a point located in the plane of the nozzle.

However, in certain installations, such as the one illustrated, it may be desirable that the burner nozzle be positioned as far away from radiation as is practical without impairing the operation of the burner. In these installations, physics of the arrangement may require that the baflie be pivoted about a point located slightly in front of the burner. The essential factor is that the bafiie be pivoted in a manner to avoid a non-uniform distribution of secondary air, and more important, a nonuniform velocity pattern.

The washer-shaped plate 86 defining a wall of the secondary air passageway is supported on the bafile 72 through the vane assembly 88 in the register opening 76 so that it pivots with the bafile 72. Preferably, a clearance 90 is provided between the plate 86 and the burner nozzle 24 to permit movement of the plate relative to the nozzle. The small amount of secondary air admitted through the clearance area will not noticeably affect the secondary air flow.

For actuating the vane assembly 88, the shaft 92 controlled by handwheel 94 is provided with a universal joint 96 for articulated movement of the shaft on movement of the secondary air passageway assembly.

Details of the support and actuating assembly for the pivoting members of the burner secondary air passageway are described in more detail in copending application S.N. 847,596 (supra).

In operation, a pulverized fuel and primary air mixture is fed to the volute entrance section of the burner and from there to the burner nozzle discharge end 18. The fuel is discharged from the burner nozzle into the combustion chamber through the burner port 40 and second-ary air is supplied under pressure through the plenum chamber 42 and secondary air passageway 73. By virtue of the ratio of register area to throat area, and by virtue of the free-flow long radius curvature configuration of the passageway, a uniform distribution of secondary air into the combustion chamber is achieved for improved flame stability.

By adjustment of one or more of the actuating rods to cause off-axial positioning of the baflie 72, the direction of flow of the secondary air and thus fuel from the nozzle outlet is changed, with a corresponding change in the direction of the flame in the combustion chamber. If it is desired to direct the flame upwardly into the combustion chamber, the lower handwheel 84 is rotated to cause the actuating rod 80 to move axially toward the combustion chamber wall to the position shown in broken lines, while the upper actuating rod (not shown) of the assembly is rotated to cause it and the upper side of the baflle to move axially away from the wall to the broken line position as shown. During this adjustment, the register area is maintained constant and uniform by virtue of movement of plate 86 with the bafile 72. Further, by pivoting the baflie 72 about a point located approximately in the plane of the burner nozzle outlet and along the axis of the nozzle, a throat area is maintained constant and uniform for optimum distribution of the second-ary air and a continued minimum pressure drop. In this respect, it is apparent that the critical ratio of register area to throat area is maintained substantially constant.

As indicated in the copending application S.N. 847,596, it has been found that the angle of change for the bafi'le 72 relative to the burner nozzle achieves an angle of change in the direction of the burner flame which is substantially the same as that of the change for the baffle and therefore only a small angular movement of the baffle is required to effect the same degree of flame movement obtained by a conventional pivotal burner.

Although the invention has been described in detail with reference to specific embodiments, it is expressly understood that th invention is not limited thereto. Other variations can be made in the arrangement of parts, as will be understood by those skilled in the art, with-out departing from the spirit and scope of the invention as defined in the following claim.

For instance, it may be possible to use for the inside surface of the secondary air passageway, an inner wall defined by a bell-shaped baffle member which is concentric with the outer bafile member 72. This inner bafiie can be arranged to pivot with the outer baffle, in the same manner as above described, to maintain a uniform passageway for the second-ary air.

What is claimed is:

A fuel burner assembly comprising:

a windbox arranged to be disposed adjacent a burner port and adapted to receive combustion air from a suitable source;

an elongated frusto-conical fuel burner nozzle having a longitudinal axis and extending through said windbox toward said burner port, the nozzle having a narrowmost outlet end adjacent said burner port for the discharge of fuel for combustion, the nozzle outlet end lying in a plane perpendicular to the nozzle axis and spaced from the burner port;

said windbox including a bell-shaped baffle means having a large circumference end remote from the burner port and a small circumferenc end terminating at the burner port separating the inside of the windbox into a plenum chamber and an elongated annular secondary air passageway encompassing the fuel burner nozzle;

the baffle means comprising a first portion co-axial with, surrounding, and spaced from the burner nozzle extending from the large circumference end substantially to the plane of the outlet end of the burner nozzle and having a long radius curvature between the large circumference end and plane of said outlet end, the baflie means further comprising an anu- "lar smooth-walled tubularflsecond p'ortion-continu ous with the first portion extending between theplane portion-having an angle of convergence sothat the surface of the second portion is approximately a parallel with the surface of the burner nozzle;

radially outward from said burner nozzle defining lwit-h the bell-shaped baffle means a circumferential opening constituting the secondary air passageway inlet and facing radially relative the burner nozzle into the plenum chamber;

a cross-sectional area proportioned so that it is approximately one and a half times the cross-sectional area of the passageway in the plane of said outlet end of the burner nozzle defined by the'bell-shaped bafiie-means and burner nozzle; I

vane means disposed in the passageway inlet end ar of said outlet'end and the 'burner port, said second i V "Washer-like" element connected to and extending 7 the inlet end of the secondary air passageway having ranged toriinpart ahelical rotational ondary air; I a the windbox and passageway being arranged for rela:

tively free unobstructed flow; I a 1 flow to the sec- References Cited 'by tih e Examiner UNITED S AT S PATENTS 2,210,476

,Vroorn 1581.5 Oberhuber V 110104 Whitney 110-404 Kidwell etal 110- 28 M-usat' t110'-2 8 Whitney'et a1. 110 28 FOREIGN PATENTS Great Britain. 

